This project is concerned with the genetic structure of the Tetrahymena macronucleus, with the mechanism of mating type determination, with the mapping of the genetic loci, both on the chromosomes and with respect to time (i.e. the time at which phenotypic assortment begins), with the mechanisms of clonal ageing, with the role of genes, and of preexisting structure in the determination of cell form, and with the comparative genetics and evolution of the tetrahymenids.